1. The Field of the Invention
The present invention relates to methods and systems for mixing fluids, namely, biological fluids.
2. The Relevant Technology
The biopharmaceutical industry uses a broad range of mixing systems for a variety of processes such as in the preparation of media and buffers and in the growing of cells and microorganisms in bioreactors. Some conventional mixing systems, including bioreactors, comprise a flexible bag disposed within a rigid support housing. An impeller is disposed within the flexible bag and is used to mix or suspend the solution within the bag. In some embodiments, the impeller is mounted to the bottom of the bag and is magnetically driven. In other embodiments, the impeller is fixed on the end of a drive shaft that projects into the flexible bag. In both embodiments, however, the impeller is designed to remain at a substantially fixed position which is optimal for mixing a narrowly defined volume of solution in the flexible bag. To enable homogeneous mixing of larger volumes of solution, larger bags are used that have an impeller positioned at a location that is optimal for that size of bag.
In some processing procedures it can be desirable to initially mix solutions at a low volume and then progressively increase the volume of the solution. For example, this is a common procedure used with bioreactors for growing cells. The process typically entails dispensing a seed inoculum in a growth media contained within a relatively small bag and then transferring the solution to progressively larger bags where additional media is added as the cells grow and multiple. This process is repeated until a final desired volume is achieved. By transferring the solution to different sized bags which each have a corresponding mixer, the operator can ensure homogeneous mixing of each of the different volumes.
Although the above process of moving solutions to different sized bags to maintain proper mixing and suspension is functional, the procedure has some shortcomings. For example, the necessity of stepping to different sized bags is labor intensive, time consuming, and has high material costs in that the multiple bags are discarded after use. Furthermore, transferring between different bags produces some mixing down-time which can influence cell growth. In addition, the necessity of shifting between bags increases the risk of contamination to the solution and potential damage to the cells.
Accordingly, what is needed in the art are improved mixing systems that solve all or some of the above problems.